1. Field of the Invention
The present invention relates to a freely deployable and/or collapsible structure and more particularly, a deployable and/or collapsible structure for use with space stations and crafts wherein its characteristics exerted when it is being deployed and collapsed have been improved.
2. Description of the Related Art
Deployable structures are usually employed on space buildings such as the space stations. They occupy a small space when they are collapsed but they become long beam-like structures when they are deployed after they are launched into space.
Various structures of this type have previously been developed. One such structure comprises plural elastic and twistable longerons and a plurality of radial spacers. The present invention is based on this structure.
The fundamental arrangement of this conventional structure on which the present invention is based will be described with reference to FIGS. 1 through 3.
FIG. 1 shows the structure deployed. FIG. 2 shows the structure under such a transient condition that it is being deployed or collapsed. FIG. 3 shows the structure collapsed. Numerals 1 and 2 represent disk-like bottom and top plates. Plural or three longerons 3, parallel to one another and having a certain interval between adjacent ones, are arranged between these bottom and top plates 1 and 2. These longerons 3 are made of elastic material such as epoxy resin reinforced with glass or carbon fibers. They are shaped like a wire having a relatively small diameter and can be elastically twisted to a spiral having a certain diameter. Both ends of each longeron are attached to bottom and top plates 1 and 2 through hinges 4 and can be freely swung round hinges 4 in the peripheral direction of bottom and top plates 1 and 2, respectively.
These longerons 3 are connected to one another by a plurality of radial spacers 5 between bottom and top plates 1 and 2. These radial spacers 5 are made of elastically deformable material such as synthetic resin and each of them is shaped like a star which has plural or three arms corresponding to the number of longerons 3 used. These arms of star-like radial spacer 5 can be elastically twisted. Radial spacers 5 are arranged in the axial direction of longerons 3 at a certain interval and foremost ends of arms of each radial spacer 5 are attached to longerons 3, respectively, to hold the latter in such a way that they are located at certain positions or tips of a regular triangle. The truss-beam-like structure shown in FIG. 1 is thus made by these longerons 3 and radial spacers 5.
A pair of diagonal cords 6 is stretched between two adjacent longerons 3 and those foremost ends of four arms of two adjacent radial spacers 5 which are connected to these adjacent longerons 3. A pair of diagonal cords 6 are similarly stretched between the lowest radial spacer 5 and bottom plate 1 as well as between the uppermost radial spacer 5 and top plate 2. These diagonal cords 6 are made of fiber material having a high tensile strength and they are flexible. Torsion rigidity and strength and flexural rigidity and strength of the beam-like structure comprising longerons 3 and radial spacers 5 are enhanced by diagonal cords 6.
Pull cord 7 is arranged in the center of the structure. One end of this pull cord 7 is attached to the center of top plate 2, for example. Through-holes 8 are formed in the center of each of radial spacers 5 and through-hole 9 is formed in bottom plate 1. Pull cord 7 extends along the longitudinal center axis of the structure, passing through these through-holes 8 and 9. The other end of pull cord 7 is connected to a winding means (not shown) attached to bottom plate 1 and it is wound or re-wound by this winding means.
When pull cord 7 is wound by the winding means, top plate 2 is rotated and longerons 3 are twisted like a coil from their top successively as shown in FIG. 2 and the structure is finally collapsed as shown in FIG. 3. If pull cord 7 is re-wound when the structure is collapsed as shown in FIG. 3, longerons 3 will extend like a straight line due to their elasticity and the structure will become deployed as shown in FIG. 1.
This structure is used for space stations, for example. The structure which is kept collapsed as shown in FIG. 3 is launched into space and then deployed as shown in FIG. 1, re-winding pull cord 7, as a structure suitable for space stations.
When the conventional structures of this type were being designed, however, consideration was paid only to the case where they are deployed from their collapsed state and then used in the deployed state. But, it is sometimes needed being again collapsed after they are deployed in space. No consideration was paid, however, to this case where they are again collapsed after being deployed. In addition, little consideration was paid to their characteristics exerted when they are under such a transient condition that they are being deployed and collapsed.
In the case of the structure shown in FIG. 1, for example, longerons 3 extend like a straight line when the structure is deployed. When this structure is to be collapsed, large load added in the axial direction of the structure is needed to buckle these line-like longerons 3 into a coil. The force of winding pull cord 7 is set large, accordingly. Further, when longerons 3 are to be transformed at their top side, there is a case where they are transformed like a coil not in a desired direction but also in a direction reverse to this desired direction. Furthermore, there is another case where they are buckled at first not at their top side but at their intermediate portion. In this last case, they are twisted like a coil at first at their intermediate portion and the structure becomes therefore extremely unstable while being collapsed. In order to solve this problem, they are previously transformed at their top side into a coil, which has a larger pitch, when the structure is under deployed state, as shown in FIG. 4. When it is arranged like this, however, the structure causes its rigidity to be substantially lowered at its top side.
When the structure is to be extended from its collapsed state shown in FIG. 1 to its deployed state shown in FIG. 3, there is a case where longerons 3 are at first erect like a straight line not at their bottom side but at their intermediate portion. In this case, the structure becomes unstable while they are being deployed, as described above. In order to solve this, it is supposed that spiral spring 11 is attached to the bottom end of each of them, as shown in FIG. 5. Torque acting in their erecting direction is thus added to their bottom ends to enable them to erect at first at their bottom side when the structure is deployed. When arranged like this, however, excessive buckling load acts on the respective bottom ends. It is also supposed that the bottom end of each of them is supported by stay 10, holding their bottom end portions previously erected like a straight line, as shown in FIG. 6. However, the structure can be collapsed only to such a state as shown in FIG. 6, so that it occupies a larger space in its axial direction when it is collapsed.
When the structure is to be collapsed, tension of one of diagonal cords 6 which are stretched like a cross is temporarily increased to a large extent and then relaxed at the initial stage of the coil-like transformation of longerons 3. Both ends of diagonal cord 6 are conventionally attached to foremost ends of the arms of radial spacers 5. Therefore, the increase in the tension of one of diagonal cords 6 caused when longerons 3 are at the initial stage of their being transformed like a coil is absorbed by excessively buckled and transformed arms of radial spacers 5. However, one end of each of diagonal cords 6 is attached to bottom or top plate 1 or 2 at both ends of the structure. These bottom and top plates 1 and 2 are high in rigidity and cannot be transformed easily. It is therefore needed that the excessive tension of diagonal cord 6 caused when longerons 3 are at the initial stage of their being transformed is absorbed by the buckling and transforming of arms of the uppermost or lowest radial spacer. This causes the arms of the uppermost or lowest radial spacer to be excessively buckled and transformed, excessive stress to be added to this radial spacer, and excessive tension to be added to the diagonal cords, as shown in FIG. 7. In order to solve this, it is supposed that those radial spacers which are located at both ends of the structure have a rigidity lower than that of the other radial spacers, but when arranged in this manner, rigidity and strength are lowered at both ends of the structure.
The present invention is therefore intended to provide a deployable and/or collapsible structure capable of eliminating the above-mentioned drawbacks caused when it is under such a transient state that the longerons are being deployed or collapsed but without losing its rigidity and strength when it is in a completely deployed state.